Part Number: TM4C129ENCPDT
Other Parts Discussed in Thread: TPS2041B
Hi
This query was actually the continuation of my previous thread - link: https://e2e.ti.com/support/microcontrollers/other/f/908/t/888744
We are updating the schematic design based on the inputs given by cb1_mobile.
We are planning to remove LDOs and use a single DC DC converter (24V dc to 3.3V dc) for powering up the microcontroller and other circuits.
We cannot isolate the GND of microcontroller and relays because of our switching ideology. Please look into the block diagram below.
Only one relay and one - shift register and ULN pair is shown in this block diagram. The no. of Shift register and ULN pair increases with relays. Approximately 256 relays i.e,., 32 qty of SR+ULN pair. But not all the relays will actuate at a time.
Isolating the SPI signal is one possible solution. But that requires addition isolating for CS pin, MR*, OE* for shift register and many other signals. We kept that as second choice.
We have also put Anti-Kickback Diodes across all relays.
The output of the shift register are pulled down with 4.7k resistor which was not mentioned in the above block diagram.
In the previous schematic image (in the link mentioned above), we have used TPS2041B for current limit.
Other than that Reverse current , Over Voltage and Short circuit protection are needed if we cannot isolate ground of microcontroller and relays.
Any other protection circuit we can implement in order to continue with the same ideology?
Thank You for your valuable time and support.
